1. Technical Field
This invention relates generally to measuring the polymer content of a material which has both polymer and cellulose components. More particularly, the invention relates to apparatus and associated methods for measuring the polymer fraction of the polymer and cellulose components by infrared absorption means.
2. Description of the Background Art
Specialty papers for use in producing such items as teabags, non-woven cloth, and other products are predominately composed of a fibrous polymer/cellulose homogeneous mixture. The polymers are added to produce qualities, such as strength, that are inadequate in other papers. Accurately measuring the polymer content of these specialty papers is an important step in controlling product quality and cost.
Previous attempts at on-line measurement of polymer content have employed radiation absorption methods wherein the absorptances of two radiation wavelengths, one of which is sensitive to the polymer, are gauged and electronically quantified, and the corresponding electronic signals appropriately processed, to measure polymer weight per unit area directly. However, these systems sometimes can provide only a crude indication of whether the polymer content of the mixture is consistent with the desired physical quality of the paper sheet. Such is the case, for example, when the primary purpose of the polymer is to bind the cellulose fibers to produce a desired degree of strength in a paper. In that case, the polymer weight (Hereinafter, the word "weight", as applied to polymer, cellulose, or both, is intended to mean weight per unit area.) by itself cannot effectively serve as a measurement of strength since it does not take into account the weight of cellulose with which the polymer is combined. Accordingly, an on-line measurement of the polymer fraction of combined polymer and cellulose weights would correlate better with laboratory tests of the physical quality than would an on-line measurement of mere polymer weight.